1. Field
Embodiments relate to a system for separating a diced semiconductor die from a die attach tape.
2. Description of the Related Art
The strong growth in demand for portable consumer electronics is driving the need for high-capacity storage devices. Non-volatile semiconductor memory devices, such as flash memory storage cards, are becoming widely used to meet the ever-growing demands on digital information storage and exchange. Their portability, versatility and rugged design, along with their high reliability and large capacity, have made such memory devices ideal for use in a wide variety of electronic devices, including for example digital cameras, digital music players, video game consoles, PDAs and cellular telephones.
While a wide variety of packaging configurations are known, flash memory storage cards may in general be fabricated as system-in-a-package (SiP) or multichip modules (MCM), where a plurality of die are mounted on a substrate in a so-called three-dimensional stacked configuration. An edge view of a conventional semiconductor package 20 (without molding compound) is shown in prior art FIG. 1. Typical packages include a plurality of semiconductor die 22, 24 mounted to a substrate 26. Although not shown in FIG. 1, the semiconductor die are formed with die bond pads on an upper surface of the die. Substrate 26 may be formed of an electrically insulating core sandwiched between upper and lower conductive layers. The upper and/or lower conductive layers may be etched to form conductance patterns including electrical leads and contact pads. Wire bonds 30 are soldered between the die bond pads of the semiconductor die 22, 24 and the contact pads of the substrate 26 to electrically couple the semiconductor die to the substrate. The electrical leads on the substrate in turn provide an electrical path between the die and a host device. Once electrical connections between the die and substrate are made, the assembly is then typically encased in a molding compound to provide a protective package.
In order to form a semiconductor package, a die bonding process is performed where a semiconductor die is diced from a wafer, picked up from an adhesive tape and bonded to a substrate. Prior art FIG. 2 shows a wafer 40 including a plurality of semiconductor die, for example die 22 (only some of which are numbered in FIG. 2). Each semiconductor die 22 on wafer 40 has been processed to include an integrated circuit as is known in the art capable of performing a specified electronic function. After testing the die 22 for bad die, the wafer may be placed on an adhesive film, referred to as a die attach film (DAF) tape, and then diced for example by saw or laser. The dicing process separates the wafer into individual semiconductor die 22, which remain affixed to the DAF tape. FIG. 2 shows wafer 40 affixed to a DAF tape 44.
In order to detach the individual die, the wafer and DAF tape are situated in a process tool, portions of which are shown in prior art FIG. 3. FIG. 3 shows a die ejector tool 50 including a vacuum chuck 52 on which is supported the wafer 40 and DAF tape 44. Chuck 52 includes a central aperture 54 over which a die 22 to be ejected is positioned. Tool 50 further includes ejector pin assembly 56 for actuating a number of ejector pins 58 up through aperture 54 and into contact with the back side of DAF tape 44. As explained below, the pins 58 push the die 22 upward so that it detaches from the DAF tape. The DAF tape may be formed of a die attach film adhered to a tape, and upon separation of the die from the tape, the film may remain affixed to a bottom surface of the die. A pick-up arm 60 is further provided to grip and complete the detachment of the die 22. The pick-up tool then transports the die 22 for attachment to the substrate or transport elsewhere.
Various chuck and pin assemblies have been implemented in the prior art to detach a die from an adhesive tape. One such configuration is shown in prior art FIG. 4, which shows a top view of vacuum chuck 52. Vacuum chuck 52 includes a plurality of openings 62 (only some of which are numbered in FIG. 4). The openings 62 are connected to a negative pressure to communicate a vacuum to the upper surface of chuck 52 in order to hold the DAF tape 44 firmly on the chuck 52. The top view of FIG. 4 also shows the aperture 54, through which the ejector pins 58 are visible. Prior art FIG. 5 is a cross-sectional view through line A-A of FIG. 4, and prior art FIG. 6 is a cross-sectional view through line B-B of FIG. 4. FIGS. 5 and 6 are provided to show that, in conventional die ejector tools, the aperture 54 is defined by perpendicular edges. That is, the sidewalls 64 of aperture 54 are perpendicular to an upper surface 66 of vacuum chuck 52.
Prior art FIGS. 7-9 illustrate the process by which semiconductor die 22 are detached from the DAF tape 44 in the tool 50. The chuck translates until a given die 22 is positioned over aperture 54. The pin assembly 56 then actuates the ejector pins 58 upward so that the pins push the tape 44 and die 22 upward. The footprint of the pins on the backside of the tape is less than the length and width of the semiconductor die, so that as the pins push the tape and die upward, the die and film delaminate from the tape. When the die 22 is mostly detached from the tape 44, the pick-up arm 60 can grab the die, for example by a vacuum at its surface, and carry the die away.
The ejector pins 58 may all rise up in concert. Alternatively, it is known to provide a multi-stage ejection, such as for example illustrated in U.S. Pat. No. 4,850,780 entitled “Pre-Peel Die Ejector Apparatus.” As shown in that patent, the chuck may include a telescopic ejector so that an outer ejector pushes the DAF tape and die upward to begin the detachment process. Next, the outer ejector remains stationary while an inner ejector, located radially inward from the outer ejector, continues upward to further separate the die from the DAF tape.
While the above-described ejector methods worked well enough in the past, die thickness have now decreased to 100 μm and thinner. At these thicknesses, the opposing forces exerted on the die by the above-described processes can break the die. For example, as shown in prior art FIG. 8, as the die 22 is pushed upward, the adhesive force of the DAF tape 44 exerts a downward force on the edge of the die. For thin die, these opposing forces may be sufficient to cause an edge 22a of the die 22 to crack or break as shown. Additionally or alternatively, as shown in prior art FIG. 9, opposing forces are similarly exerted on a semiconductor die adjacent to the die being ejected. The tape 44 under the adjacent die is held on the vacuum chuck 52, while the tape being pushed up exerts an upward force on the edge of the adjacent die. For thin die, these opposing forces may be sufficient to cause an edge 22a of the adjacent die 22 to crack or break as shown.